Recently, the situations in which a centrifugal blood pump is used for extracorporeal blood circulation in a pump-oxygenator is increasing. As a centrifugal pump, a pump of the type in which driving torque from an external motor is transmitted using magnetic coupling by completely eliminating physical communication between the external and a blood chamber in the pump to prevent invasion of bacteria and so forth is used.
An example of such a centrifugal blood pump as described above is a turbo type pump disclosed in Japanese Patent Laid-Open No. Hei 4-91396. This turbo type pump utilizes a magnetic coupling from a first permanent magnet disposed on one face of an impeller and a second permanent magnet disposed in an opposed relationship with the first permanent magnet with a housing interposed therebetween, and by rotating a rotor to which the second permanent magnet is attached, the impeller is driven to rotate. Then, although the impeller is attracted to the rotor side, since it has a groove for hydrodynamic bearing, the impeller is spaced, although only a little, away from the housing inner face by a hydrodynamic bearing effect formed between the groove for hydrodynamic bearing and the housing inner face and rotates in a non-contacting state.
Further, in the case of such a pump having hydrodynamic bearing as described above, the impeller for sending liquid is kept in a non-contacting relationship with a surrounding face by a load capacity (load capacity is a term for a bearing and has a dimension of force) generated by the groove for hydrodynamic bearing and a force counteracting the load capacity, for example, a magnetic force, thereby preventing hemolysis or formation of thrombus. Further, the load capacity varies depending upon the shape of the groove for hydrodynamic bearing. In other words, the shape design of the groove for hydrodynamic bearing is significant because this varies how great distance can be kept from the surroundings.
In a conventional hydrodynamic bearing, a logarithmic spiral shape is adopted as the shape of the groove for hydrodynamic bearing because it focuses on how the load capacity can be increased. However, in the case of a blood pump, not only is a high load capacity significant, but it is also significant that hemolysis is less likely to occur.
Therefore, the applicant of the present application proposed the pump described in U.S. Pat. No. 7,748,964 (Japanese Patent Laid-Open No. 2005-270345).
A centrifugal blood pump device 1 disclosed in this patent includes: an impeller 21 having a magnetic member 25 and rotating in a housing 20 to send blood; an impeller rotation torque generation section 3 for attracting and rotating the magnetic member 25 of the impeller 21; and grooves for hydrodynamic bearing 38 disposed on an inner face of the housing 20 on the impeller rotation torque generation section side. In each of the grooves for hydrodynamic bearing 38, a groove depth related value a (a=h1/h2), calculated from a distance h1 between the impeller 21 and the housing at a groove for hydrodynamic bearing portion upon rotation of the impeller and a distance h2 between the impeller and the housing at a groove for hydrodynamic bearing non-existing portion, satisfies 1.5 to 2.5, and a groove width related value s (s=Bo/B), calculated from a width Bo of a circumferential edge portion of the groove for hydrodynamic bearing and the sum B (B=Bo+B1) of the width Bo and a groove for hydrodynamic bearing non-existing portion width B1 between circumferential edges of adjacent ones of the grooves for hydrodynamic bearing, satisfies 0.6 to 0.8.
The applicant of the present application also proposed, in U.S. Pat. No. 7,470,246 (Japanese Patent Laid-Open No. 2004-209240), to chamfer a groove for hydrodynamic bearing such that a portion of the groove for hydrodynamic bearing which forms an angle has an R of at least 0.05 mm or more.
Hemolysis is less likely to occur in the case of the blood pumps described in U.S. Pat. No. 7,748,964 and U.S. Pat. No. 7,470,246, but further investigative efforts have led to the discovery of blood pumps able to inhibit or prevent hemolysis with a higher degree of certainty.